Batch and semi-continuous anaerobic digestion of food waste in a dual solid–liquid system

•Anaerobic digestion in a dual solid–liquid (ADSL) system was examined.•The ADSL system overcame several disadvantages of single-step digestion.•The methane production was enhanced by 13.6% in ADSL system with oil separation.•The optimum C/N and lower oil content explain the improved methane production.

To avoid the inhibition from both of waste oil and high concentrations of cationic elements, anaerobic digestion of food waste in a dual solid–liquid (ADSL) system was examined in this present paper. Results from batch test indicated that a higher methane yield could be obtained in the ADSL system. The methane yield of food solid waste (FSW), food liquid waste (FLW) and raw food waste (RFW) were 643, 659 and 581 mL/g-VS, respectively. In semi-continuous anaerobic digestion, the optimum organic loading rates (OLR) for FSW, FLW and RFW were 9, 4 and 7 g-VS/L/d, respectively. The total methane production of RFW and ADSL systems, based on 1 kg-VSRFW, were 405 and 460 L, respectively, indicating that the methane production increased by 13.6% in the ADSL system. The optimum C/N ratio, redistribution of metal element and lower content of waste oil in FSW explain the higher methane production.